It is known to coat active substances with excipients to protect them from external influences or, particularly in the case of pharmaceutically active substances intended for oral administration, to mask their taste. Although a coating material may be applied to a final dosage formulation such as a tablet, it is often much more effective if each particle of the active substance is individually encapsulated in an appropriate excipient, thus retaining the taste masking effect even on disintegration of the tablet or on administering the particles in another form such as a suspension.
Many processes are known by which to coat solid particles of active substances, such as drugs, with excipients. Generally these involve at least two stages, firstly preparing the “core” active substance particles and secondly applying the coating layer for instance by spraying. It can be difficult in such cases to control the thickness and uniformity of the applied coating layer. Moreover its application increases the size of the overall particles, which in turn can have a detrimental effect on the release profile of the active substance on subsequent administration. Thus, many known taste masking technologies produce relatively large particles which are slow to dissolve, have an unpleasant “mouth feel” and take a long time to clear from the buccal cavity.
Also known are single-step processes by which an active substance “core” and a coating material are coprecipitated as particles from liquid carriers, for instance using a supercritical or near-critical fluid anti-solvent as in the processes disclosed in WO-96/00610 (see pages 20 and 21) and WO-02/38127.
It would be desirable to be able to produce individually coated solid particles of active substances, in particular pharmaceutically active substances, which though sufficiently well coated to be taste masked are nevertheless sufficiently small in size to have a high bioavailability and a fast release rate on administration. Such active/excipient coformulations can be expected to be of particular value in producing oral dosage forms of unpleasant tasting drugs where rapid release of the drug into the patient's bloodstream is required. Effective taste masking can be of special importance when formulating drugs for administration to children and/or to the elderly.